Modern commercial and military aircraft are equipped with auxiliary power units (APUs) that provide power to operate non-propulsion systems and to start the main/propulsion engines. For example, APUs are commonly used to provide aircraft with electrical power for operating aircraft avionics and lighting, and with pneumatic pressure for cabin cooling/heating systems and for starting the main/propulsion engines. As such, APUs are regularly run before takeoff and after landing, and sometimes during flight.
Aircraft APUs burn significant amounts of jet fuel during use, generally between 40 and 100 gallons per hour of use, depending on the type of unit. Recent studies by the airline industry and military aircraft operators have shown that APUs are operated regularly and routinely even when they are not needed. Because of the high cost of jet fuel, typical operation of APUs is thus very and unnecessarily expensive. In addition, most older aircraft types do not have the ability to monitor APU use, and newer aircraft types are unable to record or transmit APU usage data when the on-aircraft avionics bus is turned off, which is when much of the inappropriate APU use occurs. Thus, actual APU use cannot be easily determined.
Consequently, APU maintenance intervals are often approximated based on aircraft hours of use. But over time the estimated APU usage can vary significantly from the actual usage. As a result, aircraft APUs are sometimes maintained too frequently, resulting in unnecessary expenses, and sometimes not maintained often enough, which can result in APU damage or failure.
Accordingly, there exists a need for improvements that facilitate more efficient use and maintenance of aircraft APUs. It is to the provision of solutions to this and other problems that the present invention is primarily directed.